The disclosures of Japanese Patent Application Nos. HEI 11-314284 filed on Nov. 4, 1999 and 2000-137880 filed on May 10, 2000, including the specifications, drawings and abstracts are incorporated herein by reference in their. entirety.
1. Field of the Invention
The present invention relates to a fuel storage apparatus and an abnormality diagnostic method of the apparatus, and, more particularly, to a fuel storage apparatus that purges fuel vapor formed in a fuel tank that is divided into a fuel chamber and an air chamber by a partition membrane, and an abnormality diagnostic method of the apparatus.
2. Description of the Related Art
A known fuel vapor process apparatus that purges fuel vapor formed in a fuel tank into an intake passage to prevent emission of fuel vapor from the fuel tank into the atmosphere is disclosed in, for example, Japanese Patent Application Laid-Open No. HEI 10-184464. The fuel tank has a deformable partition membrane that separates an internal space of the fuel tank into a fuel chamber and an air chamber in a tightly closed fashion in order to reduce the occurrence of fuel vapor. The fuel vapor process apparatus has a canister for adsorbing fuel vapor from the fuel tank, and a purge control valve for controlling the open/close state between the canister and the intake passage. When the purge control valve of this apparatus is opened during operation of the internal combustion engine, negative pressure is introduced into the intake passage, so that air flows from the fuel tank toward the intake passage. In this case, together with flow of air, fuel adsorbed in the canister is purged toward the intake passage. Hence, the above-described fuel vapor process apparatus is able to supply fuel vapor formed in the fuel tank into the engine as a fuel without letting it out into, the atmosphere.
However, if the partition membrane of the fuel tank has a hole, or if the piping connected to the fuel chamber has a crack or a disconnected pipe, fuel may leak from the fuel chamber into the air chamber due to such an abnormality, so that there is a danger of emission of a portion of the fuel vapor into the atmosphere. Therefore, in the fuel tank divided into the fuel chamber and the air chamber by the partition membrane, it is necessary to diagnose whether there is fuel leakage from the fuel chamber to the air chamber. The proportion of fuel vapor to the amount of gas pre sent in the air chamber (hereinafter, referred to as xe2x80x9cvapor concentrationxe2x80x9d) is relatively low when there is no fuel leakage from the fuel chamber to the air chamber. The vapor concentration becomes relatively high if fuel is leaking from the fuel chamber to the air chamber. Therefore, as a technique for diagnosing whether there is fuel leakage from the fuel chamber to the air chamber, it is conceivable to detect the vapor concentration in the air chamber.
In order to secure good exhaust emissions from an internal combustion engine, it is necessary to keep the actual air-fuel ratio at a value near the theoretical air-fuel ratio. If fuel vapor formed in the fuel tank is supplied to the engine, the air-fuel ratio shifts to a fuel-rich side. In that case, therefore, the fuel injection duration set for the fuel injection valve of the engine is corrected in the decreasing direction by an amount of time corresponding to the amount of fuel vapor supplied to the engine. As the vapor concentration in the gas supplied to the engine increases, the rich tendency of the air-fuel ratio continues for an increased length of time, so that the amount of decrease correction of the fuel injection duration increases. Therefore, by detecting the air-fuel ratio after fuel vapor from the fuel tank is supplied to the engine, it becomes possible to detect the vapor concentration in the gas supplied from the fuel tank side to the engine.
Therefore, as a technique for detecting the vapor concentration in the air chamber, it is conceivable to interrupt purge of fuel adsorbed in the canister toward the intake passage, and to purge gas from the air chamber directly into the intake passage, bypassing the canister, and detect the air-fuel ratio afterwards. With the vapor concentration in the air chamber detected, it becomes possible to determine whether there is fuel leakage from the fuel chamber to the air chamber.
However, if the above-described fuel vapor process apparatus is used for a long time, the vapor concentration in the air chamber becomes high in some cases because the amount of fuel vapor that permeates through the partition membrane and flows into the air chamber increases. Furthermore, if the canister for adsorbing fuel is saturated, fuel adsorbed in the canister may flow back into the air chamber, thereby increasing the vapor concentration. Still further, in a construction in which the vapor concentration is detected based on the air-fuel ratio as described above, when the engine is in a transitional state, the air-fuel ratio considerably fluctuates, so that it becomes impossible to accurately detect the vapor concentration in the air chamber.
Therefore, if under the above-described condition, it is determined whether there is fuel leakage from the fuel chamber to the air chamber based on the vapor concentration in the air chamber as described above, there is a possibility of false determination that there is fuel leakage from the fuel chamber to the air chamber when there is actually no fuel leakage from the fuel chamber to the air chamber caused by an abnormality in the system, such as a hole in the partition membrane, a disconnected pipe, etc.
Accordingly, it is an object of the invention to provide a fuel storage apparatus capable of preventing a false determination regarding the presence/absence of fuel leakage from a fuel chamber to an air chamber in a fuel tank.
In accordance with a first aspect of the invention, a fuel storage apparatus includes a fuel tank divided into a fuel chamber and an air chamber by a partition membrane, concentration detecting means for detecting a fuel vapor concentration in the air chamber based on a change in an air-fuel ratio occurring when gas is purged from the air chamber toward an intake passage of an internal combustion engine, and fuel leakage determining means for determining whether there is a fuel leakage from the fuel chamber to the air chamber based on a result of detection by the concentration detecting means. It is determined by the fuel leakage determining means whether there is a fuel leakage from the fuel chamber to the air chamber, while a predetermined operational state of the internal combustion engine is maintained.
In this aspect, the determination by the fuel leakage determining means as to whether there is fuel leakage from the fuel chamber to the air chamber is performed under a condition that the predetermined operational state of the engine is maintained. That is, if the engine is in a transitional state, the determination regarding the presence/absence of fuel leakage is not performed. Therefore, at the time of determination regarding the presence/absence of fuel leakage from the fuel chamber to the air chamber, no fluctuation in the air-fuel ratio is caused by the situation where the engine is in the transitional state, so that it becomes possible to accurately detect the fuel vapor concentration in the air chamber. Hence, according to the invention, it is possible to prevent a false determination regarding the presence/absence of fuel leakage from the fuel chamber to the air chamber.
In accordance with a second aspect of the invention, a fuel storage apparatus includes a fuel tank divided into a fuel chamber and an air chamber by a partition membrane, concentration detecting means for detecting a fuel vapor concentration in the air chamber based on a change in an air-fuel ratio occurring when gas is, purged from the air chamber toward an intake passage of an internal combustion engine, and fuel leakage determining means for determining whether there is a fuel leakage from the fuel chamber to the air chamber based on a result of detection by the concentration detecting means. When the internal combustion engine is in a transitional state, determination by the fuel leakage determining means as to whether there is a fuel leakage from the fuel chamber to the air chamber is prevented.
In this aspect, when the engine is in the transitional state, the determination by the fuel leakage determining means whether there is fuel leakage from the fuel chamber to the air chamber is prohibited. Therefore, according to the invention, it is impossible to prevent a false determination regarding the presence/absence of fuel leakage from the fuel chamber to the air chamber attributed to the situation where the engine is in the transitional state.
In accordance with a third aspect of the invention, a fuel storage apparatus includes a fuel tank divided into a fuel chamber and an air chamber by a partition membrane, concentration detecting means for detecting a fuel vapor concentration in the air chamber based on a change in an air-fuel ratio occurring when gas is purged from the air chamber toward an intake passage of an internal combustion engine, and fuel leakage determining means for determining whether there is a fuel leakage from the fuel chamber to the air chamber based on a result of detection by the concentration detecting means. The fuel leakage determining means determines whether there is a fuel leakage from the fuel chamber to the air chamber based on the fuel vapor concentration in the air chamber detected by the concentration detecting means after gas is discharged out of the air chamber.
In this aspect, fuel vapor may flow from the fuel chamber into the air chamber, permeating through the partition membrane, in some cases. If in such a case, the determination regarding the presence/absence of fuel leakage from the fuel chamber to the air chamber is performed, there is a danger that it may be falsely determined that there is fuel leakage from the fuel chamber to the air chamber caused by fuel permeation or the like when no fuel leakage is actually caused by an abnormality in a system that includes the partition membrane and the like.
When there is fuel leakage from the fuel chamber to the air chamber caused by an abnormality in the system, the fuel vapor concentration in the air chamber will become high again within a short time after gas is discharged out of the air chamber. In contrast, when fuel is flowing from the fuel chamber into the air chamber merely due to permeation through the partition membrane or the like, the fuel vapor in the air chamber will not become high within a short time after gas is discharged out of the air chamber. Therefore, in this aspect, the determination by the fuel leakage determining means as to whether there is fuel leakage is performed based on the vapor concentration in the air chamber detected after gas is discharged out of the air chamber. The vapor concentration in the air chamber after gas is discharged out of the air chamber is not affected by fuel that permeates through the partition membrane, or the like, but assumes a value corresponding to the presence or absence of fuel leakage from the fuel chamber to the air chamber caused by an abnormality in the system. Therefore, in this aspect, it is possible to prevent a false determination regarding the presence/absence of fuel leakage from the fuel chamber to the air chamber even when fuel is flowing from the fuel chamber into the air chamber, permeating through the partition membrane.
In the aforementioned aspects, the xe2x80x9cfuel leakage from the fuel chamber to the air chamberxe2x80x9d refers to leakage of fuel from the fuel chamber to the air chamber caused by an abnormality in the system, such as a hole formed in the partition membrane, a crack formed in the piping connected to the fuel chamber, a disconnected pipe in the piping, etc.
As the outside temperature increases, or as the vehicle speed decreases, the temperature of the fuel tank becomes more likely to rise, so that fuel vapor becomes more likely to be formed in the fuel tank. Furthermore, with increases in the duration during which the vehicle is stopped, or with increases in the duration during which the purge from the air chamber toward the intake passage is stopped, the amount of fuel evaporating from the fuel chamber increases. In this respect, the amount of fuel that flows from the fuel chamber into the air chamber due to a factor other than the fuel leakage caused by an abnormality in the system, for example, permeation through the partition membrane or the like, fluctuates in accordance with the conditions of the fuel tanks, the vehicle, etc.
When it is considered that the vapor concentration in the air chamber has become high due to permeation through the partition membrane or the like, there is a danger of a false determination that there is fuel leakage from the fuel chamber to the air chamber if the duration of discharge of gas out of the air chamber is not long, that is, the amount of gas discharged out of the air chamber is not great, so that the air chamber still contains an amount of fuel attributed to permeation through the partition membrane or the like. Conversely, when it is considered that the fuel chamber in the air chamber has become low, fuel in the air chamber attributed to permeation through the partition membrane or the like is quickly discharged even if the duration of discharge of gas out of the air chamber is short, that is, if the amount of gas discharged out of the air chamber is small. Therefore, based on the fuel vapor concentration in the air chamber afterwards, it becomes possible to accurately determine whether there is fuel leakage from the fuel chamber to the air chamber caused by an abnormality in the system.
In the aforementioned aspect, the fuel storage apparatus may further include concentration increase degree detecting means for detecting a degree of increase in the fuel vapor concentration in the air chamber caused by a factor other than the fuel leakage from the fuel chamber to the air chamber. The fuel leakage determining means determines whether there is a fuel leakage from the fuel chamber to the air chamber based on the fuel vapor concentration in the air chamber detected by the concentration detecting means after an amount of time corresponding to the degree of increase detected by the concentration increase degree detecting means elapses following a start of discharge of gas out of the air chamber.
Furthermore, in this aspect, the fuel storage apparatus may further include concentration increase degree detecting means for detecting a degree of increase in the fuel vapor concentration in the air chamber caused by a factor other than the fuel leakage from the fuel chamber to the air chamber, wherein the fuel leakage determining means determines whether there is a fuel leakage from the fuel chamber to the air chamber based on the fuel vapor concentration in the air chamber detected by the concentration detecting means after an amount of gas discharged out of the air chamber after a start of discharge of gas out of the air chamber reaches an amount corresponding to the degree of increase detected by the concentration increase degree detecting means.
As the outside air temperature increases, the temperature of the fuel tank becomes more likely to increase, so that fuel vapor becomes more likely to be formed in the fuel tank, as mentioned above. Therefore, even where there is no fuel leakage caused by an abnormality in the system, the amount of fuel flowing from the fuel chamber into the air. chamber permeating through the partition membrane increases and the vapor concentration in the air chamber increases with increases in the outside temperature.
Therefore, in the aspect mentioned above, the concentration increase degree detecting means may detect the degree of increase in the fuel vapor concentration in the air chamber caused by the factor other than the fuel leakage from the fuel chamber to the air chamber, based on an outside air temperature.
In this aspect, the fuel storage apparatus may further include fuel injection increasing means for increasing an amount of fuel injected into the internal combustion engine when purge of gas from the air chamber to the intake passage is started. This construction is effective in avoiding remarkable fluctuations in the air-fuel ratio during execution of determination regarding a membrane hole in the partition membrane.
In this aspect, the fuel vapor concentration in the air chamber is normally low. Therefore, if gas is purged from the air chamber toward the intake passage, the air-fuel ratio is highly likely to shift to the fuel lean side, so that deterioration of exhaust emissions becomes highly likely. Therefore, when the purge of gas from the air chamber toward the intake passage is started, it is appropriate to correct the amount of fuel injected beforehand so that the air-fuel ratio is kept at a theoretical air-fuel ratio after the start of the purge.
In this aspect, when the purge of gas from the air chamber to the intake passage is started, the amount of fuel injected into the engine is increased. Therefore, according, to the invention, it is possible to avoid remarkable. Fluctuations in the air-fuel ratio when gas is purged from the air chamber toward the intake passage under a condition that the vapor concentration is low.
In this case, the fuel injection increasing means may increase the amount of fuel injected, if the air-fuel ratio is on a lean side after the purge of gas from the air chamber to the intake passage is started.
Furthermore, in the aforementioned aspect, the fuel injection increasing means may increase the amount of fuel injected, by reducing an amount of decrease correction of the amount of fuel injected.
In accordance with a fourth aspect of the invention, a fuel storage apparatus includes a fuel tank divided into a fuel chamber and an air chamber by a partition membrane, concentration detecting means for detecting a fuel vapor concentration in the air chamber based on a change in an air-fuel ratio occurring when gas is purged from the air chamber toward an intake passage of an internal combustion engine, and fuel leakage determining means for determining whether there is a fuel leakage from the fuel chamber to the air chamber based on a result of detection by the concentration detecting means. The fuel leakage determining means determines whether there is a fuel leakage from the fuel chamber to the air chamber, by comparing the fuel vapor concentration in the air chamber detected by the concentration detecting means with a threshold that is changed in accordance an outside air temperature.
In this aspect, the determination by the fuel leakage determining means as to whether there is fuel leakage from the fuel chamber to the air chamber is performed by comparing the vapor concentration in the air chamber with the threshold that is changed in accordance with the outside air temperature. As the outside air temperature increases, the temperature of the fuel tank becomes more likely to rise, so that fuel vapor becomes more likely to be formed in the fuel tank. Therefore, even where there is no fuel leakage caused by an abnormality in the system, the amount of fuel that flows from the fuel chamber into the air chamber permeating through the partition membrane increases and the vapor concentration in the air chamber increases with increases in the outside air temperature. However, in this aspect, when the vapor concentration in the air chamber becomes high due to a high outside air temperature, the above-described fuel storage apparatus changes the threshold for determination regarding fuel leakage. Therefore, it is possible to prevent a false determination regarding the presence/absence of fuel leakage from the fuel chamber to the air chamber.
In accordance with a fifth aspect of the invention, a fuel storage apparatus is provided which includes a fuel tank divided into a fuel chamber and an air chamber by a partition membrane, concentration detecting means for detecting a fuel vapor concentration in the air chamber based on a change in an air-fuel ratio occurring when gase is purged from the air chamber toward an intake passage of an internal combustion engine, fuel leakage determining means for determining whether there is a fuel leakage from the fuel chamber to the air chamber based on a result of detection by the concentration detecting means, and refueling detecting means for detecting whether fuel has been supplied to the fuel tank by refueling. In the fuel storage apparatus, when the refueling detecting means determines that the fuel has been supplied to the fuel tank by refueling, the fuel leakage determining means determines whether there is a fuel leakage from the fuel chamber to the air chamber, based on a fuel vapor concentration in the air chamber which is detected by the concentration detecting means after gas in the air chamber is discharged to the outside thereof.
In the above aspect of the invention, whether fuel has been supplied to the fuel tank by refueling is determined. When fuel was supplied to the fuel tank through refueling of the vehicle, a large amount of fuel vapor arises, and the fuel vapor concentration in the air chamber is increased even if no fuel leaks from the fuel chamber into the air chamber. Under this situation, therefore, it is not appropriate to determine whether fuel leaks from the fuel chamber into the air chamber.
According to the above aspect of the invention, the fuel leakage determining means determines whether there is a fuel leakage from the fuel chamber to the air chamber, based on a fuel vapor concentration in the air chamber which is detected after gas in the air chamber is discharged to the outside. The fuel vapor concentration in the air chamber measured after the gas in the air chamber is discharged to the outside is not greatly influenced by refueling, but depends upon the presence of fuel leakage from the fuel chamber into the air chamber due to an abnormality in the system. Accordingly, even in the case where fuel was supplied to the fuel tank by refueling, a false determination on the presence of fuel leakage from the fuel chamber into the air chamber can be prevented.
If the fuel tank is supplied with fuel, the fuel is accumulated in the fuel chamber, resulting in an increase in the volume of the fuel chamber and a reduction in the volume of the air chamber. Meanwhile, where a negative pressure is introduced into the air chamber, the pressure within the air chamber comes to be settled at a certain negative pressure in a relatively shorter time when the volume of the air chamber is smaller. Namely, the smaller the volume of the air chamber, the shorter the period of time required for the pressure in the air chamber to reach the certain negative pressure. Accordingly, whether fuel was supplied to the fuel tank or not (i.e., whether refueling took place or not) can be determined by calculating the time required for the pressure within the air chamber to reach the certain negative pressure after introduction of a negative pressure into the air chamber.
In one preferred form of the above aspect of the invention, the fuel storage apparatus may further include negative-pressure introducing means for introducing a negative pressure into the air chamber. In this case, the refueling determining means may determine whether fuel has been supplied to the fuel tank by refueling, based on a period of time that ranges from a point of time at which the negative pressure begins to be introduced into the air chamber, to a point of time at which the pressure within the air chamber reaches a predetermined negative pressure.
If a certain amount of gas in the fuel chamber is discharged, the fuel vapor concentration in the air chamber is not greatly influenced by fuel vapors caused by refueling, but becomes equal to a value that depends upon the presence of fuel leakage from the fuel chamber into the air chamber due to an abnormality in the system. Thus, even if fuel is supplied to the fuel tank by refueling, a false determination on the presence of fuel leakage from the fuel chamber into the air chamber can be prevented.
In another preferred form of the invention, when the refueling detecting means determines that the fuel has been supplied to the fuel tank by refueling, the fuel leakage determining means determines whether there is a fuel leakage from the fuel chamber to the air chamber, based on a fuel vapor concentration in the air chamber which is detected by the concentration detecting means after an accumulated value of discharge amounts of gas in the air chamber to the outside thereof reaches a predetermined value.
In order to purge the air chamber to a certain extent after refueling was conducted, the amount of gas discharged from the air chamber needs to be increased with an increase in the fuel vapor concentration in the air chamber.
Accordingly, the fuel storage apparatus according to the above aspect of the invention may further include predetermined value changing means for changing the above-indicated predetermined value depending upon the fuel vapor. concentration in the air chamber that is detected by the concentration detecting means, when the refueling determining means determines that fuel has been supplied to the fuel tank by refueling.